1. Field of the Invention
This invention relates to windows and more particularly to windows having built-in intrusion alarm systems.
2. Description of the Related Art
Intrusion alarms for windows and doors are typically designed so that window or door movement from a closed position actuates the alarm. Usually a switch is closed by the movement to initiate the alarm as disclosed in U.S. Pat. No. 3,742,479 to Williams. This arrangement requires, in the case of windows, disabling the alarm before opening the window for ventilation purposes or for cleaning. When such windows are opened for ventilation, there is no alarm protection against intruders.
In some prior art proposals, after a window is opened and an alarm is sounded, reclosing the window discontinues the alarm. When a potential intruder opens such a window the alarm may quickly be shut off by the intruder closing the window. In such circumstances a prowler might not be frightened away by the alarm and the prowler's presence not adequately signalled.
Some window alarms are mounted on the window frame. See, for example, U.S. Pat. No. 4,472,709 to White and U.S. Pat. No. 3,378,830 to Patrick. This can result in an unsightly window and may permit tampering with the exposed alarm system by an intruder. Some alarms are constructed to be installed within an existing door or window. For example, see U.S. Pat. No. 3,768,087. Here an installation job is required to place the alarm and tools are necessary to remove the alarm for maintenance or repair.
In the case of double hung windows and so-called "slider" windows, the latter constructed from two horizontally slidable sashes disposed in a common frame for sliding movement past each other, built-in alarms could sometimes be circumvented. For example in double hung windows, the alarm components were sometimes mounted in, or on, the lower sash and the frame, respectively. The sash could be raised sufficiently to enable ventilation without tripping the alarm; but not high enough to admit a prowler without an alarm. In this condition of the window, the possibility existed that the upper window could be forced downwardly far enough to allow entry by an intruder without tripping the alarm. In most installations this kind of alarm circumvention was quite unlikely, yet remained possible.
The present invention provides a new and improved single hung, double hung or slider type window having an intrusion alarm system enabling a window sash to be opened for ventilation without triggering an alarm and wherein further opening of the window without triggering an alarm is precluded.